The spray painting of automobile bodies, truck engines, appliances, and other industrial goods is customarily carried out in enclosed areas called paint spray booths (PSB). These booths act both to contain any fumes or oversprayed paint, to reduce the chances of dust contamination, and to protect the painters. These booths vary in size, but are somewhat basic in their design and operation. A typical booth would thus consist of a work area, back section with mist eliminators, and a sump.
The units to be painted generally pass through the work area while an air flow makes the oversprayed paint contact either the sump water or the spray from the water curtain. The air is scrubbed with recirculated water at the water curtain, passes through the mist eliminators, and is removed by an exhaust fan.
Even though paint transfer efficiencies have increased through improved application technologies, roughly one-half of all paint sprayed does not reach its intended article. As a result, a significant concentration of paint builds in the system and agglomeration can occur. The resultant mass is a sticky, tacky material, which can plug the mist eliminators, shower heads, and even recirculating pumps. When this happens, scrubbing efficiency decreases, leading to potentially hazardous conditions of unchecked paint emissions being discharged into the atmosphere. Such conditions may also present severe safety hazards to paint spray booth operators.
This process involves other problems. These tacky organic deposits are subject to bacterial growth and fungi proliferation, which conditions generate corrosion and odor problems. In addition, the paint solids that are recirculated can form suspensions in the water. They remain tacky and can create expensive separation and disposal problems.
These problems show, therefore, the desirability to treat PSB water systems so as to reduce or prevent as much as possible the agglomeration and deposition of oversprayed paint on critical PSB operation parts; to render the resultant sludge non-tacky and easily removable; and to provide a water quality such that it can be recycled for use in the system.
Another problem associated with paint detackification and separation from the paint spray booth water wash system is the disposal cost associated with removal of the resulting paint sludge. For economic reasons, it is highly desirable to provide a PSB chemical treatment that results in a high solids (low moisture) sludge with a reduced or low volume sludge so that disposal costs may accordingly be minimized.